Electric switch gear



Nov. 28, 1950 G. KILMINSTER 2,532,172

ELECTRIC SWITCH GEAR Filed July 29, 1948 INVEN TOR BY g5 AGENT.

Patented Nov. 28, 1950 ELECTRIC SWITCH GEAR George Kilminster, Birmingham, England, as-

signor of one-half to Ega Electric Limited, Wednesbury, England Application July 29, 1948, Serial No. 41,321 In Great Britain August 2, 1947 4 Claims. 1

This invention relates to electrical overload switches and is concerned with overload switches for operation in electrical circuits having a plurality of ccnducting leads in each oi": which the presence of an overload current is required to actuate the switch.

The invention is specifically concerned with electrical overload switches of this kind which comprise a plurality of bi-metal strips, one strip being associated with each of said conducting leads and being adapted to bend when subjected to temperature change, a plurality of heating windings one being associated with each strip and being secured in proximity to each strip so that a proportion of the heat developed in the winding is transmitted to the strip, overload switch contacts and an operating member common to all said bi-metal strips and having a lost motion connection with the free end of each strip, said operating member being supported so as to move the overload switch contacts relatively to each other when moved through the operation of one of said lost motion connections, the winding associated with each strip being adapted to carry a current varying with that in each of said respectively associated leads.

The object of the present invention is to provide a new or improved construction in which alternative overload settings are made available without adding to any appreciable extent to the complication and manufacturing cost of the device.

A specific embodiment of the present invention is illustrated in the accompanying drawings, wherein:

Figure 1 shows in side elevation and partly in section a view of an electrical overload switch constructed in accordance with the invention;

Figure 2 is a plan view of the overload switch shown on line 22 of Figure 1.

Referring firstly to Figure 1 of the drawings, the overload switch comprises for a three-phase electrical switch three bi-metal strips IE], i i and I2 having end portions [3, l4 and i5 bent at right angles to form attachment lugs by means of which the strips are secured with screws I6, I! and E8 to a base member is formed of a block or sheet of insulating material.

Conveniently the strips it, H and 12 extend through holes 48 formed in the base member l9, and the lugs are secured within a recessed part 39 formed in the outer face of the base member i9, and the screws Hi, i! and 18 are secured within internally-threaded sleeves 5t disposed within holes formed in the base member,

. 2 the inner ends of these sleeves receiving overload terminal screws 5|, 52, 53.

It will be understood that if the overload switch is constructed as an individual unit the base member l9 may be individual to the switch. If the switch is applied to a low-tension electrical switch of the type illustrated in Figure 2 the base member l9 may support the bi-metal strips in common with other components of the lowtension electrical switch.

The bi-metal strips are disposed side by side and parallel to each other and are spaced apart in line in the direction in which the bi-metal strips can bend.

Each of the strips is provided with a heating winding, such as that seen at 20, wound on an insulating former 2|, which may be formed of asbestos or other suitable heat resisting material enveloping the bi-metal strip, the whole being covered by an outer insulating sheet 22, also of suitable heat resisting insulation.

The end portion of each bi-metal strip which is remote from the secured end is somewhat narrower than the remaining portions of the strip so that there exists between the end portion 23 and the remaining portions of the strip a pair of shoulders 24 forming abutments for the support of an overload switch contact operating member, as will be later described.

In line with the bi-metal strips, and also secured to the base member l9, are provided a pair of overload switch contact supporting strips 25 and 26, the former, 25, being more or less rigid in nature so that its associated overload contact 21 can be regarded as a fixed contact, and the latter 26 being formed of a suitable resilient material, for example phosphor bronze, so that its associated overload contact 28 can be separated from the contact 27, or allowed to move towards and into contact with the contact 2?, as desired. Normally, the strip 26 urges the contact 28 towards the contact 21 under spring pressure, due to the resilient nature of the material from which the strip 26 is constructed.

The unsecured end portion of the strip 26 is engaged by the end face 29 of an overload contact operating member 30 in the form of a bar having spaced openings Si in which engage the end portions 23 of the bi-metal strips, the bar extending lengthwise in the in-line direction in which the bi-metal strips are disposed.

At theother end of the bar a retaining member is provided in the form of a more or less rigid metal strip 32 of similar form to that which supports the fixed overload contact 21, one end of the strip being secured to the base member [9 by means of a screw.

The openings 3| in the bar 30 are wider than the width of the bi-metal strips 10, II and I2 in the lengthwise direction of the bar, that is to say in the direction in which the bi-metal strips are adapted to bend under the influence of heat transmitted to' themfrom their respective heating windings.

With the overload switch contacts 21 and 28 in the made position, as shown in Figure 1, with the end face 29 of the bar engaging the strip 26 there exists between each of the bi-metal strips and that Wall of their respectively asso-- ciated openings in the bar which they are adapted to engage when heated a clearance space 33 so that the temperature of any one 'ofthe bi metal strips has to be raised to a certain value before engagement between this wall of the opening and the strip takes place, and hence before the bar is'moved endwise to open thecontacts 21 and 28. The engagement between these walls 34 of the openings 3! and their respectiveubi meta'l strips thus constitutes a lost-motion connection betweenithe strips and the bar.

The end portion 35 of the-bar- 39 which is of somewhat difierent length, as shown in Figure 1 ber comprising a bar extending lengthwise along said in-line: direction of the bi-metal strips having a piuralitybf spaced openings one associated with each bi-metal strip into which openings a portion of each such strip extends, said openings being wider than the width of the strip in the is shorter than the end portion 36 so that the end face 31 has a different spacing from the walls 38 of the openings 31 thanthe corresponding spacing of the end face 29 of the walls 34. 'As aresult it is possible to reverse the, position of the: bar 38' on the'bi-metal strips sorthat the end face 3'! is in operative engagement with-the strip 26, and'the: bi-metal strips in bending under'heat transmitted from their windings: ze engage the walls 38 instead of the walls 3 3 of;their associated openings 31 in the bar.

.In the. preferred construction illustrated it will beapparent thattthe. contacts of the strips 26 and are securedinsomewh-at different. positionsrelative toatheends of their respective-strips soxthatsth'ey engage each other correctly. The unsecured .end: of each of the contact supporting strips: 251andi 25 isibent' over at fright angles and lies parallel: 13013116. side faces of..tha bar 30, the two: bent-oversendaiportionsof the strips being spaced apart: by thezthicknessof the bar so as to form a guideiforthe end of the bar which operatively engages theizmovable strip- 26,11 Likewise .thezbentr-over: end dl oil-the retaining member 32;. serves tolprevent the. bar becoming displaced from the bi-metal stripsrin' any position-inwhich the whole'overlo'ad switch assembly maybe held.

;,.Individual: terminal screwsuar'ei provided for each winding: 28 of the bi-metal strips, these-terminal screws being indicated at 32, the other end of the winding being brought out tothe: terminal screws 5!, 52 and 53: already referred to.

iAn' outer casing 63' isprovided to; protect the bi metal strips, the bar andoverload' contact-,the casing having a peripheral flangei isa-by means of which it is screwed with screws t'othe-supportingbase I9.

:WhatIclaimthenis:

:laAn electrical overload switch foran electrical". circuit: having a plurality of conducting leads. in: each: of:.which the presenceof an overload current is requisredi-to actuate. the switch, said overload switch comprising-a plurality of bimetal strips, arranged. substantially parallel to each other and side by side spaced: apart in line inathedirection in: which they are adapted; to bend,supportingmeans for, the strips, at least direction in which increase of temperature causes the strips to bend, said bar being adapted to move the overload switch contacts relatively to each other in endwise movement of the bar in one direction, by engagement of an abutment on the bar with means for moving said contacts relatively, each of said strip portions being spaced from that wall or its respective bar opening towards which the strip bends when subjected to an'increase in temperature, each of said strips being adapted to bend to engage said wall and move said bar in the said direction to move the switch contacts when heated by an overload cur-- rent of the required value in its associated winding, and said bar'being provided with anabutment at each end one such abutment having a spacing lengthwise along the bar from the-walls of said openings engaged by said strips in bending different from the spacing of the other abutment from the walls of opening opposed to those aforesaid, whereby reversal of the bar to change from use of one abutment'to theother results in a variable overload setting.

2. An electrical overload switch for an elec-- trical circuit having a plurality of conducting leads in each of which the presence of an overload current is required to actuate the switch, said overload switch comprising a plurality of bi-metal strips securedupon an insulating base member, and arranged substantially parallel to each other and side by side spaced apart in line in the direction in'which they are adapted to bend, at least one stripbei-ngassociated with each of said conducting leads, said bi-metal strips being adapted to bend when subjected to temperature change, aheating winding woundon each strip and insulated electrically therefrom, the winding associated with each strip being adapted to carry a current varying with thatin each of said respectively associated conducting leads, overload switch contacts, an overload switch contact operating member comprising a'bar extending. lengthwise along said-'in-line directionof the bi-metal strips having a plurality of spaced-open ings one associatedwith each bi-metal strip into which openings, a portion of each such strip'extends, said openings being'wider than the width of the strip in the direction in which'increa'se of temperature causes the strips to bend, said 'bar being adapted to move the overload switch contacts relatively to each other in endwise movement of the bar in one direction, each of said stripportions bein spaced from that wall of its respective bar opening towards which the strip bends when subjected to anincrease in temperature, each of said strips being adapted to bend 7 to-engage said-wall and move said bar in the said direction to move the switch contacts when heated by an overload current of the required value in its associated winding, the abutments on the bar being constituted by the end faces thereof which engage in operation directly against a resilient metal strip carrying one of the overload switch contacts, said resilient metal strip being secured at one end to said base mem her, the other of said overload switch contacts being carried by a second metal strip secured at one end to said base member and disposed sub stantially parallel to the other said cont-actcarrying strip, the unsecured end of each of said contact-carrying strips being bent over to lie parallel to side faces of the bar and constituting a guide for the end of the bar operatively engaging movable contact-carrying strips.

3. In an electrical overload switch of the kind in which, for operating a pair of overload switch contacts, there is provided, a plurality of bimetal strips having heating windings, and arranged substantially parallel to each other'side' by side spaced apart in line in the direction in which they are adapted to bend on the presence of a current in their heating windings; an overload switch contact operating bar common to all said bi-metal strips, said bar having for selective insertion between the bi-metal strips and the overload switch contacts at least two sets of longitudinally spaced abutments, each set including one abutment for co-action with the overload switch contacts, and spaced from it by distances less than the normal separation between the bi-metal strips and the overload switch contacts, abutments for engagement by each strip establishing a lost motion connection between the former and the latter, the spacing between the abutment for engaging and operation the overload switch contacts and those for engagement by each strip being different in one set as compared with the other set to provide at least two overload settings.

4. In an electrical overload switch of the kind I metal strips having heating windings, and arranged substantially parallel to each other side by side spaced apart in line in the direction in which they are adapted to bend on the presence of a current in their heating windings; an overload switch contact operating bar common to all said bi-rnetal strips, said bar having for selective insertion between the bi-metal strips and the overload switch contacts, two sets of longitudinally spaced abutments, one set including one abutment at one end of the bar for co-action with the overload switch contacts and spaced from it by distances less than the normal separation between the bi-metal strips and the overload switch contacts, abutments for engagement by each strip establishing a lost motion connection between the former and the latter, the other set including at the other end of the bar one abutment for co-action with the oyerload switch contacts and spaced from it by distances less than the normal separation between the bi-metal strips and the overload switch contacts but different from those pertaining to the first said set, abutments for engagement by each strip, and means supporting the bar removably in relation to the bi-metal strips and the overload switch contacts whereby it can be reversed end to end to bring into operation one or the other set of abutments.

GEORGE KILMNSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,365,782 Hartwig Jan. 18, 1921 1,871,875 Bradford Apr. 16, 1932 2,253,390 Muller Aug. 19, 1941 FOREIGN PATENTS Number Country Date 501,885 Great Britain Mar. 7, 1939 

